1. Field of the Invention
The invention relates to a torque detecting method and an arm device.
2. Description of Related Art
When servo control is performed on a single-axis arm, using force (torque) detected with a torque sensor, compensation needs to be made in view of the effect of self-weight torque, mechanical deviation arising upon mounting of the torque sensor, frictional force produced during rotation of the arm, and so forth.
A gravity compensation method of a control system that performs force control is disclosed in Japanese Patent Application Publication No. 62-60010 (JP 62-60010 A). According to the gravity compensation method of JP 62-60010A, a gravity coefficient for an arm angle is calculated in advance, based on the mass of the arm and the position of the center of gravity of the arm. Then, during operation of the arm, gravity compensation torque is obtained, using the gravity coefficient corresponding to the arm angle, and gravity compensation is made using the gravity compensation torque.
However, in the gravity compensation method described in JP 62-60010 A, there is a need to accurately grasp the mass of the arm and the position of the center of gravity of the arm, so as to correctly compensate for the self-weight torque (gravitational torque) of the arm which changes according to the angle of the arm. This process may be cumbersome.